摘要详情
294 / 2023-02-17 15:41:15
Life Cycle Assessment of Upcycling CO2 Pre-treated Waste Slags in Cement Paste: Comparative Study between Yellow Phosphorus Slag and Basic Oxygen Furnace Slag
yellow phosphorus slag; basic oxygen furnace slag; dry carbonation; aqueous carbonation; life cycle assessment; sensitivity analysis
摘要录用
Mineral carbonation is considered to be an effective method to convert solid wastes, such as yellow phosphorus slag (YPS) and basic oxygen furnace slag (BOFS), into valuable products for the construction industry. The mineralization process can be conducted directly under dry (DC) or aqueous (AC) conditions. However, the slow reaction and low CO2 fixation efficiency of DC and high water consumption required for AC are the key challenges for large-scale applications. In this study, we evaluated the environmental impact of carbonation of YPS and BOFS via dry and aqueous routes, and the upcycling of these CO2 pre-treated waste slags in cement paste production.
The environmental impacts from materials preparation to blended cement paste manufacturing (cradle-to-gate) were quantified by life cycle assessment (LCA), which consists of the following two system boundaries (Fig. 1):
System boundary 1: DC and AC of YPS and BOFS;
System boundary 2: Using carbonated YPS/BOFS and raw YPS (raw-YPS) to replace cement at ratios of 10% and 20%.
According to the midpoint assessment results (Fig. 2), the GWP value of AC was 11% and 214% lower than that of DC for YPS and BOFS, respectively. This is mainly due to the long duration and significantly lower CO2 uptake of DC. As seen, the emissions from the operation process can nearly be offset by the positive impact of BOFS due to the considerable amount of CO2 that can be captured and avoided disposal of the waste in landfill (BOFS recovery). This reduced CO2 emission is particularly obvious in the case of AC, which reaches ~187 kg of negative CO2 emissions. In terms of human carcinogenic toxic (HCT), no significant difference can be observed in the DC and AC of YPS, as it is a non-toxic substance. While the recycling of BOFS is of great significance to reduce HCT, due to metal precipitation and other problems in the landfilling process, which remains the main reason for the huge difference between YPS and BOFS in mineral resource scarcity. The higher liquid-to-solid (L/S) ratio of AC for YPS leads to a higher water consumption which is 3 times of BOFS.
Results of endpoint assessment (Fig. 3) showed that carbonation of BOFS causes lower impacts compared to YPS in all three categories, mainly associated with the recovery of BOFS leading to the avoidance of a large amount of metal ion precipitation in the landfill process. The fine particulate matter formation potential of carbonation of YPS is significantly higher than that of BOFS, since the longer carbonation duration the higher consumption of additional electricity, which has a large impact on human health.
Cement production has the highest contribution (over 90%) for GWP in the manufacturing process of blended cement paste (Fig. 4). However, as carbonated slags contribute less than 10% of total emissions, only 6-14% of carbon emissions can be reduced even if the replacement rate increases from 10% to 20%. Replacing cement with 20% aqueous carbonated YPS (AC-YPS) shows no effect on strength, but can reduce GWP by 11%. As for BOFS, the addition of dry carbonated (DC-BOFS) and aqueous carbonated BOFS (AC-BOFS) showed a quite similar effect on the compressive strength of cement paste, while 20% of AC-BOFS cement paste exhibited the lowest carbon footprint, approximately 24% reduction compared to OPC paste.
Keywords: yellow phosphorus slag; basic oxygen furnace slag; dry carbonation; aqueous carbonation; life cycle assessment; sensitivity analysis
The environmental impacts from materials preparation to blended cement paste manufacturing (cradle-to-gate) were quantified by life cycle assessment (LCA), which consists of the following two system boundaries (Fig. 1):
System boundary 1: DC and AC of YPS and BOFS;
System boundary 2: Using carbonated YPS/BOFS and raw YPS (raw-YPS) to replace cement at ratios of 10% and 20%.
According to the midpoint assessment results (Fig. 2), the GWP value of AC was 11% and 214% lower than that of DC for YPS and BOFS, respectively. This is mainly due to the long duration and significantly lower CO2 uptake of DC. As seen, the emissions from the operation process can nearly be offset by the positive impact of BOFS due to the considerable amount of CO2 that can be captured and avoided disposal of the waste in landfill (BOFS recovery). This reduced CO2 emission is particularly obvious in the case of AC, which reaches ~187 kg of negative CO2 emissions. In terms of human carcinogenic toxic (HCT), no significant difference can be observed in the DC and AC of YPS, as it is a non-toxic substance. While the recycling of BOFS is of great significance to reduce HCT, due to metal precipitation and other problems in the landfilling process, which remains the main reason for the huge difference between YPS and BOFS in mineral resource scarcity. The higher liquid-to-solid (L/S) ratio of AC for YPS leads to a higher water consumption which is 3 times of BOFS.
Results of endpoint assessment (Fig. 3) showed that carbonation of BOFS causes lower impacts compared to YPS in all three categories, mainly associated with the recovery of BOFS leading to the avoidance of a large amount of metal ion precipitation in the landfill process. The fine particulate matter formation potential of carbonation of YPS is significantly higher than that of BOFS, since the longer carbonation duration the higher consumption of additional electricity, which has a large impact on human health.
Cement production has the highest contribution (over 90%) for GWP in the manufacturing process of blended cement paste (Fig. 4). However, as carbonated slags contribute less than 10% of total emissions, only 6-14% of carbon emissions can be reduced even if the replacement rate increases from 10% to 20%. Replacing cement with 20% aqueous carbonated YPS (AC-YPS) shows no effect on strength, but can reduce GWP by 11%. As for BOFS, the addition of dry carbonated (DC-BOFS) and aqueous carbonated BOFS (AC-BOFS) showed a quite similar effect on the compressive strength of cement paste, while 20% of AC-BOFS cement paste exhibited the lowest carbon footprint, approximately 24% reduction compared to OPC paste.
Keywords: yellow phosphorus slag; basic oxygen furnace slag; dry carbonation; aqueous carbonation; life cycle assessment; sensitivity analysis
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深圳大学
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